docs: def get_balance_in_period(self, start: Datum, end: Datum):
          """
          Calculates the balance for the given time period.
          The balance is taken to be 0 at the beginning of the period and then all the
          transactions are added together until the end date/time.
          """
          assert isinstance(start, Datum)
          assert isinstance(end, Datum)
  
          total = Decimal(0)
  
          splits = self.get_splits_in_period(start, end)
  
          for split in splits:
              total += split.quantity * self.account.sign
          return total